Preheat oven to 200C. Cook macaroni in a large saucepan of boiling water following packet directions or until al dente, adding cauliflower and broccoli in the last 2 mins of cooking. Drain well.

Meanwhile, heat a large saucepan over medium-high heat. Cook bacon, stirring, for 3 mins or until crisp. Use a slotted spoon to transfer to a plate. Melt butter in pan. Add flour and cook, stirring, for 2 mins or until mixture bubbles and is grainy. Reduce heat to low. Gradually add milk. Cook, stirring constantly, for 5 mins or until the sauce boils and thickens. Remove from heat. Stir in the cheddar. Season.

Stir in the macaroni mixture and bacon. Spoon into a large baking dish. Bake for 20 mins or until golden brown and heated through.